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RHESSI Science
Principal Investigator Robert Lin explains sun science and RHESSI mission
objectives. Featuring
satellite data and images of the Sun.
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LIN: The sun, as you know, provides light and heat and so forth for the Earth, and it's very, very stable.
That's mostly in white light, and at other colors or other wavelengths the sun varies quite a bit in
its emissions. Sunspots are concentrations of the magnetic field of the sun. Watching these
sunspots, you notice that every eleven years you get more sunspots, and so that was how the original
solar maximum and minimum were defined.
So solar maximum is the time when the sun's emissions, its radiation, in these other colors is much
stronger than at minimum for reasons that we don't understand , when we get very strong magnetic
fields of the sun than these other phenomena, like these explosions or flares, and the increase in the
amount of radiation in different wavelengths at different colors like extreme ultraviolets all
increase because solar flares are really gigantic explosions, the most powerful explosions in the
solar system. But they're much, much more energetic than any of the atomic or hydrogen bombs that
exploded on Earth. The sun releases this energy in a very short time, a time scale of seconds to
minutes. How it does that nobody understands. It seems to have to do with the strong magnetic fields
of sunspots.
The other interesting fact that we learned is that when it releases its energy, a large fraction of
this energy of the explosion energy, goes into accelerating hydrogen carbons. Again this is something
we don't understand - how can the sun accelerate these high energy particles so efficiently and so
rapidly? So right now at Berkeley, we are building what's called HESSI, or High Energy Solar
Spectroscopic Imager. That spacecraft is designed to look at the most energetic radiations of all the
very hard X-rays, gamma rays, and this will be the first time that those very energetic, most
energetic, radiations have been imaged from the Sun basically from anywhere.
Back to HESSI Mission Info.